ESTRO 37 Abstract book

S128

ESTRO 37

Acute RTOG grade 3-4 toxicity (urinary and/or intestinal) were recorded in 1 of 63 patients of RR cohort (1.5%) and early severe postoperative complications were documented in 5 patients (8%) of RP cohort. Late RTOG grade 3-4 toxicity (urinary and/or intestinal) were recorded in 7 of 63 patients of RR cohort (11.1%) vs. 11 patients of PRT cohort (17.4%) (p=0.05). Conclusion In this matched pair analysis performed in patients with HRPC features at diagnosis, RR achieves better significant biochemical control than RP without significant differences in overall and specific survival. High proportion of patients in RP cohort requires PRT achieving poor rates of biochemical control and being more toxic. PV-0255 Salvage high-dose-rate brachytherapy for previously irradiated locally recurrent prostate cancer M. Galdeano-Rubio 1 , C. Guitérrez-Miguiélez 2 , D. Najjari- Jamal 2 , I. Modolell-Farré 3 , F. Ferrer-Gonzàlez 4 , A. Boladeras-Inglada 4 , R. Gracia-Lucio 3 , J.F. Suárez-Novo 5 , J. Pera-Fàbregas 2 , F. Guedea-Edo 4 1 Hospital Sant Joan de Déu-Fundació Althaia, Radiation Therapy Department, Manresa, Spain 2 Institut Català d'Oncologia - Hospital Duran i Reynals, Radiation Therapy Department - Brachytherapy Unit, Barcelona, Spain 3 Institut Català d'Oncologia - Hospital Duran i Reynals, Medical Physics Department, Barcelona, Spain 4 Institut Català d'Oncologia - Hospital Duran i Reynals, Radiation Therapy Department, Barcelona, Spain 5 Hospital Universitari de Bellvitge, Urology Department, Barcelona, Spain Purpose or Objective External Beam Radiotherapy (EBRT) is considered the standard practice for localized prostate cancer. Although this, local relapses are not uncommon and the ideal savage treatment is not well-defined. We report our outcomes in terms of efficacy and safety of salvage high- dose-rate brachytherapy (HDR-BT) for locally recurrent prostate cancer (LRPC) after definitive radiation therapy (RT). Material and Methods From august 2004 to december 2016 we retrospectively analyzed 96 patients undergoing HDR-BT after pathological confirmation of LRPC. The median age at diagnose was 67 years (55-78) and, the median PSA was 4’1 ng/ml (1’27-19). Gleason score and T scale were 7 and T2, respectively. Prescribed total dose was 38Gy. Patients received 4 fractions of 9’5Gy with 2 implants spaced 2 weeks. The 6% of the patients received previous hormonal therapy (HT) and 11% received adjuvant HT. Biochemical failure (after receiving both primary EBRT and/or BQT) was based on Phoenix definition. Acute and late genitourinary and gastrointestinal toxicities were documented based on Common terminology criteria for adverse events (v4.0). Median follow-up after HDR-BT was 44 months (3-138 months). Results At the time of this study the 3 and 5-year biochemical relapse free rate were 61% (74-42, 95% CI) and 31% (45- 17, 95% CI) respectively. The 5-year local and regional relapse rate were 21% (33-8, 95% CI) and 16% (26-6, 95% CI) respectively. The 5-year systemic relapse rate was 18% (30-6, 95% CI). The 5-year disease free survival was 54% (68-40, 95% CI). The 5-year cancer specific survival rate was 94% (100-88, 95% CI). Late genitourinary Grade 3 and 4 were 12% and 2% respectively, including 8 prostate necrosis. 18 patients required urinary catheter, five required transurethral resections and 2 required cistocath. Conclusion Salvage prostate HDR-BT is an effective modality for LRPC after EBRT although toxicity is not negligible. We

propose lower total doses for further treatments and a properly selection of patients through MRI and PET to avoid overtreatment in metastatic patients. PV-0256 Fast and insightful bi-objective HDR prostate brachytherapy planning N.H. Luong 1 , T. Alderliesten 2 , B.R. Pieters 2 , A. Bel 2 , Y. Niatsetski 3 , P.A.N. Bosman 1 1 Centrum Wiskunde & Informatica, Life Sciences & Health, Amsterdam, The Netherlands 2 Academic Medical Center - University of Amsterdam, Radiation Oncology, Amsterdam, The Netherlands 3 Elekta, Elekta Brachytherapy, Veenendaal, The Netherlands Purpose or Objective The goal in prostate brachytherapy (BT) planning is to select the best trade-off between target coverage and organ sparing. Searching for the set of best possible trade-off plans has great potential because it facilitates planners to insightfully compare plans and select the most appropriate plan for each patient. To find such plans automatically, we introduce a bi-objective optimization model that describes separate objectives for target coverage and organ sparing. Dose-volume indices (DVIs) are key in planning. DVIs are typically computed using randomly sampled dose calculation (DC) points. For final evaluation, many points are used for the sake of accuracy, e.g., Oncentra Brachy (Elekta) uses by default 500,000 points. For optimization, typical automated BT planning methods (e.g., IPSA, HIPO), use about 100 times less points for the sake of speed. We studied the relation between the number of DC points and the quality of plans obtained with our bi- objective approach and studied whether a novel multi- resolution scheme can reduce the total planning time. Material and Methods We derived separate coverage and sparing objectives based on DVIs of a clinical protocol (Table 1). To solve this bi-objective optimization model, we used the Gene- pool Optimal Mixing Evolutionary Algorithm (GOMEA). For each of 18 HDR prostate BT cases, we conducted 5 experiments: 4 with 2,500, 5,000, 10,000, and 20,000 DC points and 1 with a multi-resolution scheme in which the number of points is gradually increased during optimization from 5,000 to 20,000. Final results were re- evaluated using 500,000 DC points. The quality of the obtained set of plans was scored by the hypervolume indicator, which quantifies the area covered by the set of plans. We compared the DVIs of the automatically generated plans with the clinical plans that were obtained in 30-60 minutes by experienced planners using IPSA/HIPO, followed by graphical optimization.

Results Using fewer DC points, better hypervolume scores are obtained in the first 5-10 minutes. More points lead to better results, but it takes longer to achieve good plans. Differences between using 5,000 and 20,000 DC points are substantial, signifying that for successful bi-objective optimization, more DC points are needed than for single- objective optimization (e.g., IPSA and HIPO). Using the